Packing block with high adsorption capacity for gaseous effluent purification device

ABSTRACT

The invention relates to a packing block made by alternately stacking thin corrugated plates (P1, P3) with a first elongation direction (X1), thin corrugated plates with a second elongation direction (X2) different from the first, and sheets (2) made of a material adsorbing the contaminants, interposed between the various thin plates in this stack. Such a block is used to pack the units of a purification device and is disposed in a stream of effluents containing contaminants such that the effluents pass through the channels delimited by the corrugations of the corrugated plates and the interposed sheets.

The present invention relates to a device with an adsorbent structurethat can be placed in a gaseous effluent stream in order to retaincontaminating substances that are mixed therein.

The process and device according to the invention can be applied inparticular for purifying gaseous effluents containing volatile organiccompounds, hereinafter called VOC, malodorous substances, or water. Thegeneric term VOC includes hydrocarbons, chlorinated, fluorinated, andchlorofluorinated compounds, NOx compounds, SOx compounds, H₂ Scompounds and mercaptans, NH₃ compounds and amines, and in general, allorganic and inorganic compounds that may be present in troublesomeconcentrations in the air for various reasons.

Patent EN. 95/10591 by the applicants teaches a device for eliminatingcontaminants mixed with gaseous effluents. The effluents to be purifiedpass through a barrier comprising an array of purifying units side byside in an enclosure, each of which units contain adsorbing materialssuch as activated charcoal or zeolites. To restore the purifying abilityto the purifying units, they are selectively and successively isolatedby means of a movable collector when their adsorbent content issaturated, the time necessary for their desorption by heating and fortransfer of the substances by an auxiliary fluid (a fraction of theeffluents in the stream for example or a gas brought selectively to theinlet of the purifying unit to be desorbed by an auxiliary circuit), andpossibly the substances mixed with the auxiliary fluid are transferredto a reactor designed to eliminate them.

Each purifying unit has for example several flat compartments disposedparallel or accordion-fashion between the front and rear faces of thepurification barrier, with a space between them. Each of thecompartments is delimited laterally by pieces of perforated sheet metaland is filled with an adsorbent material such as activated charcoal forexample. Certain inlets and outlets on the front and rear faces areclosed in order to lengthen the path of the effluents and thus increasetheir surface contact with the adsorbent. This deflection of flow canalso be achieved by sheet metal baffles disposed slantwise between thevarious compartments or by disposing the compartments zigzag fashionsuch that the effluent is compelled to pass through them.

It is known that columns can be provided for heat or substance exchangebetween the fluids or for filtering, with multi-channel packings. Thesepackings can be made on the basis of honeycomb structures or be made bystacking or juxtaposition of sheets or plates with a periodic structure(corrugations or differently shaped deformations) which delimit thechannels in which the fluids circulate. Adsorbent materials can beplaced in the channels of the packing to purify the fluids.

Packings for columns, possibly with adsorbing materials, are describedfor example in the following patents: EP-229,199 (U.S. Pat. No.4,675,103), U.S. Pat. No. 4,532,086, EP-117,949 (U.S. Pat. No.4,541,967), U.S. Pat. No. 4,744,928, EP-640,385, U.S. Pat. No. 4,672,536or U.S. Pat. No. 4,830,792.

In the remainder of the text, the expression "corrugated plate" will beused to designate in general any plate provided with periodic lengthwisedeformations that are parallel to each other (with a common elongationdirection).

The packing block according to the invention is designed to adsorbcontaminating substances mixed into a stream of gaseous effluents. Ithas at least one block made by stacking thin corrugated plates with afirst elongation direction alternately with thin corrugated plates witha second elongation direction, different from the first. Thecorrugations delimit two nonparallel channel networks.

It is characterized in that the two networks communicate with each otherthrough sheets made of a material adsorbing the contaminants, interposedbetween the various thin plates in this stack, the block being disposedin a stream of effluents such that the effluents pass through it atdepth, circulating randomly between the two channel networks andremaining in contact with the adsorbent sheets.

According to one embodiment facilitating periodic desorption of theblock by countercurrent thermal action of the streams to bedecontaminated, the thin corrugated plates are made from a materialcapable of reflecting infrared rays and the adsorbent material is chosenfor its considerable ability to adsorb infrared rays.

The thin corrugated plates can be made from inorganic or organicmaterials. As the case may be, the thin corrugated plates may be madefrom smooth metal or metal with discontinuities or roughnesses:perforated, stamped, and crimped metal sheets, sheet metal, etc. inorder to create turbulence favoring contact between the effluents andthe sheets of adsorbent material.

The adsorbent sheets can be made of one or more layers of activatedcharcoal cloth or fiberglass cloth coated with an adsorbent substancesuch as hydrophilic or water-repellent zeolites, as the case may be, ornonwovens such as felts for example.

With a packing block designed in this manner, the effluents pass throughthe packing block following the channel delimited by the folds in theplates and remain in intimate contact with the adsorbent sheets. Thedesorption obtained is very effective without a high pressure lossresulting thereby.

Other characteristics and advantages of the packing block according tothe invention will emerge from reading the description hereinbelow ofembodiments described as nonlimiting examples with reference to theattached drawings wherein:

FIG. 1 shows schematically, in cross section, a stack of corrugatedplates and adsorbent sheets;

FIG. 2 is a top view of superimposed corrugated plates with symmetricalelongation directions relative to an axis X0 on either side of anadsorbent sheet;

FIG. 3 shows schematically a packing block made by stacking plates andadsorbent sheets.

As shown in FIGS. 1 and 2, the block is made by stacking thin plates P1,P2, P3, P4, etc. provided with periodic lengthwise deformations parallelwith each other such as corrugations. For a first set of corrugatedplates (odd plates P1, P3, etc. for example) the elongation direction ofthe corrugations is X1. The elongation direction X2 of the corrugationsof the complementary set of plates (even plates P2, P4, etc.) makes anangle 2α with direction X1. The angle α can vary for example between 5°and 45° for example. The inclination of the successive plates in thestack relative to each other has the effect that they are in contact bytheir tops or edges without risk of fitting into each other.

Sheets 1 made from a material chosen to adsorb the contaminants in theeffluents to be treated, or from a substrate on which an adsorbentsurface is mounted, are interposed between all the plates (P1, P2,),(P2, P3), (P3, P4) etc. Each sheet 1 delimits, with each of the adjacentcorrugations, a triangular passageway 2. These adsorbent sheets arepreferably made of materials able to withstand high temperatures(several hundreds of °C.) necessary for their thermal desorption.

A block or packing 3 is made from such a stack of corrugated plates Pwith interposition of adsorbing sheets 1 (FIG. 2) and can be used forexample in the purifying units of the device in the aforementionedpatent application EN 95/10591. Block 3 is positioned for example suchthat the directions X1, X2 of the channels on either side of adsorbentsheets 1 are symmetrical with each other relative to the main directionX0 of a stream of effluents to be purified. With this arrangement, thelength of the paths traversed by the effluents along passageways 2 isincreased.

Adsorbent sheets 1 can for example be activated charcoal cloth and be inone or more layers, or be fiberglass cloth coated with water-repellentzeolites. They can also be made on the basis of felt or any othernonwoven material that adsorbs throughout its mass, or by its coating.

The thin corrugated plates P are metal or polymer sheets able towithstand the temperatures necessary for periodic desorption of theadsorbent. These plates can be smooth, but preferably haveirregularities of relief, roughnesses, or discontinuities in order to inparticular to create turbulent flow of the effluents along passageways 2and improve their contact with sheets 1 resulting in better absorptionof the contaminants. This effect is obtained with plates having a finedistribution of holes, embossed and stamped plates, or plates made of afolded cloth.

Blocks can be made (FIG. 3) with adsorbent sheets of activated charcoalcloth with a thickness th disposed between corrugated or folded plateswith a pitch s, and fold thicknesses t between the folds, in thefollowing dimensions:

2≦e≦6 mm

10≦s≦20 mm

0.5≦ep≦3 mm

and in this way make blocks in which the mass of activated charcoalcloth is between 50 and 150 kg per m³ for example.

If plates P made of a material that reflects infrared waves and sheets 1made of a substance well able to adsorb these waves (as is the case foractivated charcoal cloth for example) are used, so-called countercurrentthermal desorption can be carried out. Downstream of each purificationblock, as described in the aforesaid patent application, is a reactoremitting infrared waves which propagate well in the upstream directionalong the various passageways 2 without being impeded by the streams ofeffluents moving in the reverse direction.

A packing block has been described in an application to purification ofgaseous effluents. It would not however be a departure from theinvention to use it in another application. Such a block might serve forexample also for dehumidifying air in applications to agriculturalindustries: drying grains, etc., in which case the adsorbent sheets aremade for example on the basis of hydrophilic zeolites or any othersubstance able to adsorb water, particularly alumina.

We claim:
 1. Packing block for a purification device designed to adsorbcontaminating substances mixed into a stream of gaseous effluentscomprising a stack, made by alternately stacking thin corrugated plateswith a first elongation direction (X1) and thin corrugated plates with asecond elongation direction (X2) different from the first, with thecorrugations delimiting two nonparallel channel networks, characterizedin that the two networks communicate with each other through sheets madeof a material adsorbing the contaminants, said sheets being interposedbetween the various thin plates in this stack, the block being disposedin a stream of effluents such that the effluents pass through it atdepth, circulating randomly between the two channel networks andremaining in contact with the adsorbent sheets.
 2. Packing blockaccording to claim 1, characterized in that the thin corrugated platesare made from a material capable of reflecting infrared rays and theadsorbent material of the sheets is chosen to adsorb infrared rays. 3.Packing block according to claim 1, characterized in that the materialadsorbing contaminants of the sheets comprises at least one layer of anactivated charcoal cloth.
 4. Packing block according to claim 1,characterized in that the sheets have at least one layer of a fiberglasscloth coated with hydrophobic zeolites.
 5. Packing block according toclaim 1, characterized in that the sheets have at least one layer of afiberglass cloth coated with hydrophilic zeolites.
 6. Packing blockaccording to claim 1, characterized in that the thin corrugated platesare made from cloth.
 7. Packing block according to claim 1,characterized in that the sheets have at least one layer of a nonwovensubstance.
 8. Packing block according to claim 7, wherein said nonwovensubstance is felt.
 9. Packing block according to claim 1, characterizedin that the thin corrugated plates have roughnesses or discontinuities.10. Packing block according to claim 9, characterized in that the thincorrugated plates have a hole distribution obtained by drilling,embossing, or stamping.